thickness in any area is equal to or less than the ser-
vice limit specified in
Table 1
or
Table 2
.
3. Check the disc runout as follows:
a. Make sure the disc mounting bolts are tight
prior to running this check.
b. Mount a dial indicator so its plunger sits 2-3
mm (0.09-0.12 in.) from the outside diameter
of the disc (
Figure 80
).
c. Slowly rotate the wheel and watch the dial in-
dicator. Replace the disc if runout is out of
specification.
4. A used disc will usually have some radial
grooves. If these grooves are large enough to snag a
fingernail, they will reduce brake effectiveness and
increase brake pad wear. If large grooves are evi-
dent, consider replacing the disc. The discs cannot
be machined, as the removal of material will reduce
the disc thickness below the specification.
5. If there is evidence of disc overheating due to
unequal pad pressure, inspect the following:
a. The caliper may be binding on the caliper pin.
b. The caliper piston is binding in the caliper.
c. The master cylinder relief port is plugged.
d. The master cylinder primary cup is worn or
damaged.
Removal/Installation
1. Remove the front or rear wheel as described in
Chapter Eleven.
CAUTION
Set the tire on two wooden blocks. Do
not set the wheel down on the brake
disc surface. It could be scratched or
damaged.
NOTE
Insert a piece of wood or vinyl tube
between the pads in the caliper(s).
This way, if the brake lever or pedal is
inadvertently applied, the pistons will
not be forced out of the cylinders. If
this does happen, the caliper(s) will
have to be disassembled to reseat the
pistons and the system will have to be
bled. By using the wood or vinyl tube
in place of the disc, the system will not
have to be bled when installing the
wheel.
2. Remove the brake disc bolts (A,
Figure 81
). On
a front wheel, remove the hub cover (B).
3. Lift the brake disc (C,
Figure 81
) from the hub.
4. Clean the threaded holes in the hub.
5. Clean the brake disc mounting surface on the
hub.
6. Installation is the reverse of removal. Note the
following:
a. The brake disc bolts are made from a harder
material than similar bolts used on the motor-
cycle. When replacing the bolts, always use
standard Yamaha brake disc bolts. Never
compromise and use a generic replacement.
They may not properly secure the disc to the
hub.
b. Install a disc so its arrow points in the direc-
tion of forward wheel rotation.
c. Apply a small amount of a medium-strength
threadlocking compound to the bolt threads.
BRAKES
377
13
81
80